There are known in the prior art protective helmet assemblies including relatively hard outer shells from which sound-attenuating earcup assemblies are suspended in proximity to the wearer's ear. These earcup subassemblies are made up of hard earcups provided with soft annular seals around the edges thereof for forming a seal around the ear of the wearer's head. The earcup volume and the seals have been carefully designed to attenuate ambient noise which enters the hard outer shell through the bottom thereof. Providing adequate sound attenuation in respect of ambient noise is particularly important in an environment such as that of a combat vehicle wherein the crew members must be able to communicate effectively and efficiently. It will readily be apparent that high noise levels not only are distracting and fatiguing, but in the absence of adequate attenuation may interfere with effective communication.
In order to maintain an effective seal between the wearer's head and the earcup subassembly a force must be applied to the earcup. Various suggestions have been advanced in the prior art for accomplishing this result. Most of the mechanisms rely on some direct mechanical pressure to ensure a tight seal between the earcup assemblies and the wearer's head. Such arrangements do not always provide even application of pressure with the result that the sound-attenuation is not as effective as is desired and the wearer is subject to discomfort.
Various methods of effecting the sealing described hereinabove have been employed. In one arrangement in which the earcup subassemblies are supported in a fabric assembly, a chin strap is tightened to pull the earcup assemblies into engagement with the wearer's head. Alternatively, layers of foam have been inserted between the helmet shell and the earcup. In another method a resilient strap or spring applies pressure directly to the earcup. All of these methods of the prior art involve a trial and error adjustment which requires that the helmet must be taken off and put back on a number of times until a proper fit is accomplished. This is in addition to the defects of direct pressure application discussed hereinabove.